This invention relates generally to terminator devices and in particular, it relates to a detection method and apparatus used with a bus for detecting the number of terminators connected to the bus transmission lines.
One application where reliable clam transfers are important is in the field of data transmissions on a bus transmission line for communication between a plurality of peripherals and a central processing unit in a small computer. For example, a Small Computer System Interface (SCSI) bus provides for such a communication link.
As is generally known in the art of designing bus transmission lines, a terminator, comprising of a resistor network, is typically connected to each of the physical ends of the bus in order to eliminate line reflection created by the transmission of signals on the bus. Both of the terminators have a characteristic impedance equal to that of the bus.
Many peripherals, such as disk drives, are adapted to connect to the bus. These peripherals are usually equipped with a bus terminator which is to be removed if the peripheral is not connected to one end of the bus. However, with the addition and removal of various peripherals from the bus, terminators may inadvertently be omitted or more than one terminator may be inadvertently connected to the bus.
Visual verification of the number of terminators connected to the bus normally requires the system to be mined off and the system components disassembled. However, there are prior art designs which measure the number of terminators connected to the bus, but all of these designs share the same disadvantage of requiring the computer system to be rendered inactive in order for the bus to be tested.
Therefore, there is a need for a diagnostic apparatus which has the ability to determine the number of terminators present on a bus without deactivating the computer system. The present invention is such an apparatus.
In view of the above, it is an object of the invention to determine if the bus is active. If the bus is found to be inactive, the diagnostic phase commences.
It is another object of the present invention to determine the number of terminators connected to the bus.
It is still another object of the present invention to display the number of terminators connected to the bus.
It is a further object of the present invention to provide a signal for enabling or disabling a controllable bus terminator, respectively, depending on if there are not enough or too many terminators determined to be connected to the bus.
Another object of the present invention is to provide a controllable bus terminator which is enabled or disabled, respectively, depending on if there are not enough or too many terminators determined to be connected to the bus.
Also, it is an object of the present invention to maintain the controllable bus terminator in the proper enabled or disabled mode whenever bus activity resumes.